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Concrete has naturally high compression strength — you can drive vehicles on it without crushing it. It’s tensile strength, or ability to withstand being pulled in opposite directions, is not as high. Rebar, or reinforcing bar, increases the tensile strength of the finished product.
When drilling through concrete, you may also need to drill through rebar. Follow this step-by-step guide to do so safely.
Drilling Through Concrete Rebar
When reinforced concrete is installed, steel rods are laid in a grid pattern and secured with wire ties before the concrete is poured over and around them. These steel rods have a ridged surface which helps them bind tightly to the concrete.
Drilling through concrete rebar is a lot different than simply cutting rebar. Here are step-by-step instructions.
- Personal protective equipment is necessary to protect yourself from the dangers of drilling concrete. At minimum, don a tightly-fitting respirator and eye glasses with side shields. Goggles or a full-face shield are even better. Bit breakage is common when drilling through rebar; protect your face and eyes from dangerous metal projectiles.
- Consult the size and spacing information below to determine where you are likely to encounter rebar while drilling. Choose an appropriate drill. Handheld drills, hammer drills, and rotary drills all have the capacity to drill through rebar when paired with appropriate technique and materials.
- Measure and mark the site for drilling and choose a bit for your pilot hole. You can start with a masonry bit and switch to a tungsten carbide or diamond core bit should you hit rebar. The pilot hole should be at least three to four times smaller than your desired end result.
- Place the tip of the bit against the mark you made in step three and slowly apply pressure to work the drill bit through the concrete. When the tip of the bit encounters rebar, it is possible that you will lose control of the drill. Should this happen, simply drop the drill and step back. When you release the trigger the drill will stop spinning.
- Clean the hole using a vacuum or a can of compressed air and shine a light inside. If you can’t see any rebar, it’s possible you encountered an air pocket or large rock. If you can see rebar, determine whether it is oriented horizontally or vertically. If the ridges are perpendicular to the floor, you have found a horizontal support. Parallel ridges indicate the rebar is providing vertical reinforcement.
- Drilling through rebar can weaken the overall structure of the concrete, so never take on this project without the knowledge and approval of a contractor or structural engineer. Should you encounter rebar while drilling through concrete on accident, consider moving the location of the hole. You will need to fill and seal any holes you make to prevent exposure to moisture in the air from rusting and weakening the rebar.
- If you can’t move the hole and you’re using a 4-cutter SDS drill bit, just keep drilling. The four carbide tipped blades should be able to cut through the steel bar without breaking. If you’ve chosen any other kind of masonry bit, you will need to take a break from drilling and swap out the bit. See the guide below for help choosing your accessories.
- Operating the drill at a slow and steady pace, apply pressure to encourage the bit to penetrate the rebar. The resistance will change when you’ve passed all the way through, and you can switch back to a masonry bit to complete the hole. When the hole is the depth and diameter of your choice, clean it out with a vacuum or a can of compressed air. Remember to add ¼ of an inch to the depth of the hole, to allow room for settling debris. Do not remove your respirator until the area is clear of dust.
Learn how to cut through concrete pavers in our guide.
Rebar Size and Spacing
Rebar is laid both horizontally and vertically to form a grid.
- For driveways, an 18-inch grid structure is often used.
- For a patio, 24 inches between bars is standard.
When rebar is used to support a concrete wall, the minimum recommended grid size is 36 inches. The rebar must also extend to within 18 inches of the top of the wall.
Most suppliers stock 11 standard sizes of rebar. The smallest, #3, has a diameter of ⅜ of an inch, and is commonly used to reinforce swimming pools, patios, and highways. #18 rebar is the largest standard size, measuring 2¼ inches in diameter, and is used to support large structures such as bridges.
A rebar detection tool can help you determine where rebar is placed. Like stud finders, they are not perfectly accurate, but serve as a helpful guide.
Also see our guide on how to bend rebar.
Best Bits for Drilling Through Rebar
Choosing the right drill bit is important to the success of your project. These five types of drill bits will get the job done.
Diamond is harder than steel. Metal drill bits with diamond pieces embedded in them are the industry standard for drilling through rebar. They are universally compatible and come in nearly every diameter. Diamond-core bits are the best choice when you need to make a large hole.
For smaller holes up to 1 ½ inch in diameter, tungsten carbide drill bits are an option. They are expensive and, since the technology is relatively new, are only available in a limited number of sizes.
This workhorse bit has four carbide cutting blades and is less likely to break while drilling through rebar. If you don’t want the hassle of trading out bits, a 4-cutter SDS bit is the best choice.
Steel Twist Bits
Believe it or not, regular steel twist bits are capable of drilling through rebar for a short period of time before they break. Because broken bits are so dangerous, this method is not recommended.
This specialty bit can be used to speed up the drilling process. It is designed for use in tools that can switch between rotary and hammer drilling.
Use the drill’s hammer mode to drill through the concrete, then switch to a rebar cutter and rotary mode. Once you’ve cleared the rebar, switch back to a masonry bit and hammer mode to finish the hole.
You can drill through rebar using a rotary drill, hammer drill, or regular handheld drill and an appropriate bit. Working slowly and steadily is key to achieving good results. Always wear a respirator and eye protection.